Levocetirizine (as levocetirizine dihydrochloride) is a third-generation,[1] non-sedating antihistamine, developed from the second-generation antihistamine cetirizine. Chemically, levocetirizine is simply the isolated levorotaryenantiomer of cetirizine, which is sold as a racemic mixture.

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Levocetirizine is used for allergy symptoms including watery eyes, runny nose, sneezing, hives, and itching.[2] The manufacturers claim it to be more effective with fewer side effects than previous second-generation drugs; however, there have been no published studies supporting this assertion. A study part-funded by the manufacturer UCB concluded it may be more effective than some other second- and third-generation anti-histamines, but did not compare it to cetirizine.[3]

Levocetirizine is an antihistamine. It acts as an inverse agonist that decreases activity at histamine H1 receptors. This in turn prevents the release of other allergy chemicals and increase the blood supply to the area, and provides relief from the typical symptoms of hay fever. It does not prevent the actual release of histamine from mast cells.

On 31 January 2017, the Food and Drug Administration approved Xyzal as an over-the-counter drug.[5] Although the drug was only authorized by the FDA on 25 May 2007, it was already available in most European countries. Like many new drugs it entered the market at a higher price than currently available third and second generation antihistamines. In India, one form of the drug is available as Crohist MK tablets and syrup, a formulation of levocetirizine hydrochloride and montelukast. In India, Crohist MK is a Schedule 'H' drug and may only be prescribed by a registered medical practitioner. In Finland, Hungary, China, The United States and Kuwait[6] the drug is sold over-the-counter.